The present invention relates to a print head of a dot matrix printer, and more specifically to a print head which comprises an electromagnet assembly, a number of elongated print wires, and a number of armature members, the electromagnet assembly including a number of electromagnetic core means.
In print heads of this type, an assembly including print wires and armature members is generally mounted on an electromagnet assembly by means of, for example, bolts or screws. Examples of such print heads are disclosed in U.S. Pat. Nos. 4,051,941, 4,165,940 and 4,382,701.
In such a conventional arrangement, however, maintaining assembly accuracy of essential parts is rather difficult and requires excessive labor, on account of variations in dimensional accuracy of components and errors in mounting the components. In particular, gaps between individual electromagnetic core means of the electromagnet assembly and their corresponding armature members are subject to variations, so that it is hard to obtain stable gap accuracy. With this arrangement, moreover, it is impossible to adjust the gaps. Therefore, impacts of magnetic forces applied to the individual print wires are subject to variations, lowering the print quality. Also, it is impossible to maintain uniform quality of print heads as industrial products.
Print heads are proposed which use leaf springs each provided with a number of legs or arms in place of the bolts or screws for mounting. These alternatives cannot, however, enjoy satisfactory mounting accuracy, leaving the aforesaid problems unsettled.
In the prior art arrangement, moreover, that portion of each armature member facing each corresponding electromagnetic core of the electromagnet assembly does not have an elaborate configuration, so that the degree of convergence of magnetic flux passing through the core is lowered with the advance toward the forward end of the corresponding portion of the armature member, resulting in lower magnetic flux density. Thus, in the case of a so-called attraction-type dot matrix printer in which print wires are driven by attracting armature members by excitation, it may be impossible to obtain a necessary attraction. In the case of a so-called release-type dot matrix printer in which print wires are driven by releasing armature members by deenergization, it may be impossible to obtain a necessary releasing force.
In general, the armature members are each formed of a platelike member which has two wider lateral faces and two narrower end edges. These armature members are disclosed in, for example, U.S. Pat. Nos. 4,051,941, 4,165,940 and 4,367,962. These armature members are radially arranged and their respective narrower end edges adjoin one another. Therefore, the angular intervals between the individual armature members are so wide that the number of arrangeable armature members is limited. Accordingly, the print wires used are reduced in number. Thus, it is difficult to increase the number of print dots and to miniaturize the print head. Particularly, the print heads of printers for Chinese characters, which require a relatively large number of print dots, would inevitably be increased in outside diameter.
In print heads of a type in which one end portion of each armature member and the rear end of its corresponding print wire are connected to each other, the rear end of the print wire conventionally is inserted into a fitting hole formed in the one end portion of the armature member, and is rigidly connected thereto by, e.g., brazing. According to this method, however, the connecting work is troublesome, and the joint portion is so wide that it is difficult to narrow the intervals between the radially arranged armature members. As a result, the number of arrangeable armature members cannot satisfactorily be increased. This constitutes a hindrance to the miniaturization of the print heads of the Chinese-character printers or the like which require a larger number of print dots.